Most companies keep track of their employees, their sales, inventory, etc etc.
Pretty much every website that has you log in or post content stores all that information in a big database.
Many of your activities throughout the day use databases. Here are some common examples. If you purchase something at the grocery store, the price is being looked up in a database based on the UPC...
A telephone directory. It has a bunch of information but it is all sorted efficiently to be able to find exactly what you need without having to read the whole phone book.